For a polyether glycol, which is a starting material for a polyurethane, to be used for spandex or a synthetic leather, polyoxytetramethylene glycol (hereinafter abbreviated as "PTMG"), which is a homopolymer of THF, has primarily been used. However, the soft segments of the urethane elastomer employing PTMG are liable to be crystallized at lower temperatures causing problems in physical properties such that recovery after being elongated under stress is not sufficient.
As one method for solving this problem, investigations have been made with copolymers of THF and cyclic ethers as a substitute of polyether glycols for PTMG. However, due to difficulty in ring opening polymerizability of a cyclic ether or in a synthesis of a cyclic ether, only limited species of copolymers are available and therefore no satisfactory result has yet been obtained.
In addition, ring-opening polymerizability of THF is low generally, and heretofore production of a copolymer having hydroxyl groups at both terminal ends by copolymerizing THF with a polyhydric alcohol co-presented therewith was unknown. It had only been known that epichlorohydrin, which is high in ring-opening characteristic, is allowed to co-exist with THF (see Japanese Patent Publication after examination No. 32200/1973). However, the polyhydric alcohols added in this method may be considered to act only for an initiation of the reaction, and therefore they are bonded only to one terminal end of the polymer.
The present inventors have made extensive studies to overcome the problems described above aand consequently discovered a catalyst which is capable of synthesizing a polyether glycol by copolymerizing a diol with THF to accomplish the present invention.